The bubbling bed hydrogenation technology for residual oil is an important technology for processing heavy oil with high contents of sulfur, residual carbon and metals, and has apparent advantages in solving the problems of fixed bed hydrogenation of residual oil, such as low space velocity, rapid deactivation of the catalyst, large pressure drop of the system, inclination of coking, short operation cycle of the device, etc.
For ensuring long-term operation of a bubbling bed residual oil hydrogenation device for 3-5 years, the STRONG technology for bubbling bed hydrogenation of residual oil realizes on-line charge and discharge of a catalyst. When a deactivated catalyst is discharged from a reactor, a large quantity of petroleum type pollutants (alkanes, aromatics, gums, bitumen, etc) are adsorbed on the surfaces and inside the pores of the discharged catalyst particles, which petroleum type pollutants, once put into the environment, may be extremely harmful to human bodies, animals, plants, and the air and water environment. Hence, a good number of strict regulations aiming at environmental protection have been made against catalyst discharge. The US Environmental Protection Agency (EPA) has put waste catalysts (including waste catalysts discharged from hydrogenation treatment, hydrogenation refining, hydrogenation cracking) into the list of dangerous discards. In 2008, the Ministry of Environmental Protection of PRC listed waste catalysts in the National Catalog of Hazardous Waste, and labeled their hazardous property as Grade T (toxic). On the other hand, the oil content of a discharged catalyst is usually up to 20-60%. Unreasonable treatment thereof means tremendous waste of petroleum resource.
Up to now, discharged catalysts are treated in the industrial field mainly in two ways: landfill and incineration. However, landfill may waste a lot of land resource, and cause pollution to the soil environment and the water environment. In the treatment by incineration, the heat energy in the petroleum type pollutants is not utilized effectively. In addition, because a large amount of sulfur and heavy metal components, among others, are usually adsorbed in the discharged catalysts, these components may be carried by tail gas into the air environment during incineration or calcination, forming a secondary pollution source.
Chinese Patent Application CN 1557977A disclosed a process for recovering oil by condensing a dry distillation gas which was obtained in continuous dry distillation of a discharged catalyst at 400-800° C. for 1-2.5 hours. However, the process as a whole suffered from the problems of long flow and high energy consumption. Chinese Patent Application CN 101166837A disclosed a process of stirring and scrubbing a discharged catalyst using a dense phase gas having a pressure up to 60 bars. However, there existed the problems of complex device operation, large device investment, and poor maneuverability. U.S. Pat. No. 4,661,265 disclosed a process for separating oil from a catalyst discharged from a reactor, comprising: decreasing the temperature of the discharged catalyst to the flash point of the oil using an oil cooling method; and then exporting the discharged catalyst from a storage tank using a screw conveyor, wherein the oil leaked down from the screw slit under gravity during the exporting, such that separation of oil from the discharged catalyst was realized. However, the deoiling efficiency was not high, and the discharged catalyst still contained a lot of oil after treatment.
To sum up, in general, current treatment of a discharged catalyst cannot achieve ideal effect due to insufficient deoiling efficiency, or unduly high consumption of energy for treatment, or even generation of secondary pollution. The development of hydrogenation process is affected seriously by the environmental and resource problems resulting from unreasonable treatment of discharged catalysts. In order to remove the troubles that affect the development of the bubbling bed hydrogenation process for residual oil, the issue about the treatment of a catalyst discharged from bubbling bed hydrogenation of residual oil has to be addressed. Hence, the top priority at present is development of a process and a device capable of treating a catalyst discharged from bubbling bed hydrogenation of residual oil in an effective way.
In 1993, thermal desorption was adopted by the US Environmental Protection Agency (EPA) to treat oil-containing solid waste (petroleum sludge), wherein the waste was washed repeatedly using a hot alkaline aqueous solution, followed by air floatation to carry out solid-liquid separation. Generally, the washing temperature was controlled at 70° C., the liquid/solid ratio was 3:1, and the washing time was 20 minutes. Oil field sludge containing 30% oil could be washed to contain less than 1% residual oil. In 1999, Michael J. Mann (Full-scale and Pilot-scale Soil Washing [J]. Journal of Hazardous Materials, 1999, 66:119-136) treated oil polluted soil by washing with hot water, and constructed a model device for washing soil. In the specific operation, the polluted soil particles were subjected to particle size classification using a hydraulic cyclone, and the classified polluted soil particles were washed under agitation in an agitator. As good effect was achieved, hot water washing became a relatively effective method for treating oil-containing solid waste. German Patent DE 4232455 (A1) also involved hydraulic classification of polluted soil with a hydraulic cyclone, wherein the polluted soil particles after classification were washed in a jet mixer, and the washing medium might include hot water, steam and water containing a chemical additive. However, the above processes are all directed to natural sand or clay particles as the subject of treatment, which have pore volume and specific surface area much smaller than those of an artificial catalyst support. Hu Xiaofang, et al (Relationship between Air Permeability of Soil, Specific Surface Area of Clay Particles and Fractal Dimensions of Particle Size Distribution of Clay Particles [J]. Chinese Journal of Soil Science, 2007, 38(2): 215-219) measured the specific surface area of the clay particles in the soil in South China, indicating that the BET specific surface area of the clay particles in the common soil was 39-151 m2/kg. In contrast, we can see that, if taking the catalyst support used in a bubbling bed hydrogenation process for residual oil as an example, the BET specific surface area is up to 286109.4 m2/kg. Such a large specific surface area of the catalyst particles in comparison with the clay particles suggests that the amount of the petroleum type pollutants adsorbed by the corresponding particles is much higher, and the separation by desorption is more difficult. It's difficult to treat the oil-containing porous particles of a catalyst discharged from bubbling bed hydrogenation of residual oil and having large pore volume and specific surface area using the conventional hot water washing process. Moreover, this process has a series of problems, such as complex flow, large area occupied by devices, large investment for devices, and long cycle of process operation.
Therefore, there exists an urgent need in the art for development of a process and a device for treating a catalyst discharged from bubbling bed hydrogenation of residual oil in order to solve the problems concerning the catalyst discharged from the bubbling bed hydrogenation of residual oil in a better way and fulfill the object of recovering oil from the discharged catalyst.